Most locks for bicycles comprise a chain and a padlock to prevent theft of the bicycle. Other patents disclose complicated structures mounted in the header of the front fork, such as U.S. Pat. Nos. 2,081,778 and 2,544,590. Others have locks located in the crank hanger, i.e. U.S. Pat. No. 704,655, and two have locks in the head or sleeve, U.S. Pat. Nos. 1,998,512 and 977,533. It was to overcome the deficiencies of bicycle locks that the very simple lock of the present invention was conceived.